Primary Feathers in Flight. 



15? 



indicate that the feathers had been interlocked a very short 

 time. If, however, the notches remained for a period of 

 minutes or more it would show that the feathers had been 

 interlocked for a longer time. This proved to be the case in 

 experiments which consisted of artificially interlocking the 

 emarginate primaries for different lengths of time. The 

 recovery of the semi-elastic webs of the primary feathers 

 notched by the pressure of the interlocked feathers has there- 

 fore been the subject of investigation. 



Measurements have been made which consisted in determin- 

 ing the widths of a notch at different intervals of time imme- 

 diately after the death of a hawk. For the purpose of 

 explanation, in fig. 1 the initial width of the notch is indicated 



by the distance apart of the lines A and A', and the gradual 

 diminution in its width is indicated by the notches on the 

 lines A, B, C, and D, which represent the edge of the web of 

 a primary at different intervals of time after the feathers were 

 "unlocked. 



Method of Measurement. 



The method of measurement was as follows : the points of a 

 pair of fine dividers were adjusted to correspond with the 

 width of a notch in a primary as soon as possible after a hawk 

 had been killed. Impressions of the points were then made in 

 a notebook and their distance apart afterwards determined by 

 means of a fine scale. Measurements were made every few 

 minutes in this way until the notch disappeared or ceased to 

 diminish in width. 



Am. Jour. Sci.— Fourth Series, Vol. XXI, No. 122.— February, 1906. 

 11 



